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"Fujian" TV-lens 50mm f/1.4 C-mount
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PostPosted: Sat Jul 14, 2012 8:04 am    Post subject: Reply with quote
Nordentro wrote:
fermy wrote:
Yes, the little vignette that you've shown is consistent with what I am getting on m4/3. The obvious solution to this puzzle is that there are several Fujian 50/1.4 lenses. Will post pictures of my lens later. Post yours as well when you get a chance.

here Wink


..thats exactly the lens i have..and it works fine on aps-c..at least mine does.. Shocked
..btw i got it from the vendor the picture is taken from on ebay..


PostPosted: Mon Jul 23, 2012 10:07 am    Post subject: Reply with quote
Hmmm interesting, I knew they made two very different looking lenses as I have one of these http://imgs.inkfrog.com/pix/hitechproduct/IMG_9232_001.JPG

I didn't know there was variation in lenses with the same appearance though!

I want to get one of the other type and compare them but I don't want to end up with one that doesn't cover aps-c!


PostPosted: Mon Jul 23, 2012 1:37 pm    Post subject: Reply with quote
fatdeeman wrote:
Hmmm interesting, I knew they made two very different looking lenses as I have one of these http://imgs.inkfrog.com/pix/hitechproduct/IMG_9232_001.JPG

I didn't know there was variation in lenses with the same appearance though!

I want to get one of the other type and compare them but I don't want to end up with one that doesn't cover aps-c!


Probably this one?

Click here to see on Ebay


PostPosted: Thu Jan 03, 2013 4:10 am    Post subject: Reply with quote
fermy wrote:
There must be Laughing

Ok so I took the lens apart. It's extremely easy to do from both sides. 3 screws on the mount part give access to the aperture ring. Twist the top (where the words "TV Lens" are) and the vanity ring comes off giving access to the focus ring. The construction is primitive. Instead of the usual double helicoid, the lens unit is driven by the screw that goes up ad down, which is driven by the groove on the inner side of the focusing ring. Here goes my theory that one can adjust infinity on the lens. Not possible, unless you file another groove that restricts the screw movement.

Anyway, at first I thought that vignette is caused by the vanity ring being too tall, but no, this is not the case. The vignette is there even with the vanity ring off.

I guess they've changed something in the lens at some point to allow for bigger coverage. On the other hand, the front element on my lens looks very much like the one on yours.


I have the same lens it focuses past infinity when mounted with an RJ C-PQ adapter on the Pentax Q (no vignette on the PQ - it images fine). About 16mm further past sighted infinity on the scale before it hits the stop if it is measured roughly. From a bit of browsing around and practical tests it appears from the threads per inch count that this converts to about 1 3/4 turns of the lens in the mount or 1.3-1.4mm unscrewed. Obviously if I could find a spacer to this thickness and the threads were sufficeint to grip the lens then this would allow proper infinity focus. I have tried the lens on camera unscrewing until infinity focus is found at end stop and based my theory as stated. This has to be done carefully as the lens gets quite loose on the adapter. However there is an "air-space" - threadless gap between the c-mount threads and the back flange of the lens of a similar gap. Therefore if I can find a suitable adapter the lens should tighten on it's mount properly.

I have followed the examination of the innards of the camera - front and back easily accessed and confirm that the focus movement is governed by a pin that slides on a slotted ramp cut into the front beauty-ring/hood and has no obvious means of adjustment in the normal manner of simply moving the lens stop attached to the separate aperture ring and letting the conventional helical sort it out.

However this is a considerable adjustment difference and we might wonder whether factory tolerances are so sloppy. Maybe they are. I would like to pose the possibility that the silver ring at the rear of the lens held by three set screws has something to do with infinity focus adjustment. I have tried loosening them but nothing moves easily and I am reluctant to use force. Surely I will be tempted again but in the meantime I will ask if wiser heads have had some better experience with this adjustment? My unconfirmed theory being that this ring when removed might allow the metal part of the lens to be adjusted inside the plastic housing by rotation. My theory falls rather short if this movement is sufficient that the lock ring will not longer have enough purchase surface to lock the grub screws. I need 1.3mm - might work.

The focus ring "reports" that the lens will focus to as close as 300mm but I only seem to get about something a little less than 1 metre (which would be expected given that the lens focuses past infinity at the other end of it's range).

If some way of adjusting this very nice little lens to infinity then it would be appreciated by many. Meanwhile it does provide a quite sharp infinity - then goes on and on for a while over the horizon to some little point beyond the ken of man. It is quite useable - but then I am a perfectionist, and these small things irritate.

Tom
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